Source material shot on film at 24 frames per second is translated to video (at 30 frames per second) by a process known as 3:2 pulldown. In this process every other film frame is converted to three interlaced video fields. The intervening film frames are converted to two interlaced video fields. FIG. 1A illustrates video signal originated via video processing. Each box represents a video frame. Each column of circles represents a field. Successive columns of circles represent interlaced video fields. FIG. 1B illustrates video signal originated via the 3:2 pulldown process. Each box represents a film frame of source material. For every other film frame three video fields are generated, two of which contain identical information, for example fields A and C in frame 1 are identical and fields F and H of frame 3 are identical. Being able to determine whether video material is derived via 3:2 pulldown or video processing can be used to advantage in many video signal processing systems such as IDTV receivers or digital video compression systems.
Consider video signal compression. Video signal originated from film includes one redundant field in every five fields, or a 20 percent redundancy. If the video signal can be determined as having originated in film mode, it is possible to delete the redundant fields in the compression process to achieve an 20 percent compression bonus. FIG. 1C illustrates the formation of frames of interlaced video for compression according to the MPEG (Moving Pictures Expert Group of the International Standards Organization) protocol. FIG. 1D illustrates the formation of frames of interlaced film mode video for MPEG compression wherein it may be seen that redundant fields may be excised.